Fuel tanks on board vehicles of various kinds generally have to meet leaktightness and permeability standards in relation to the type of use for which they are designed and the environmental requirements that they have to satisfy. At the present time, both in Europe and throughout the world, there is a substantial tightening of the requirements regarding the limitation of pollutant emissions into the atmosphere and into the environment in general.
To limit these emissions, care is taken in particular to position the components (ventilation lines, valves, baffles, stiffeners, etc.) inside the tank and/or the fill pipe (see in particular application WO 2004/024487 in the name of the Applicant). However, when these components are fastened to the tank after it has been molded, it is generally necessary to make at least one opening in the tank so as to be able to introduce said components into the tank and to fasten them thereto. Hence there may be potential leakage problems near this opening.
Several years ago the Applicant therefore developed a process of initially molding a cut parison (cut into two sections) in order to be able to introduce thereinto and fasten thereto components during the actual molding of the tank and to thus avoid drilling openings (see Patent EP 1 110 697 in the name of the Applicant).
This process has since been the subject of several improvements targeting particular means for fastening these components: see in particular Applications WO 2006/008308 (fastening of components by rivet punching), WO 2006/095024 (fastening of ventilation lines that have a part that can be deformed due to the presence of a bend that is stretched during the attachment of these lines to the parison) and WO 2007/000454 (fastening of components according to an ideal layout and in particular, as regards the ventilation lines, while avoiding the formation of siphons).
These improvements have been able to be made due to the use of a core i.e. a part of suitable size and shape for being able to be inserted between the cavities of the mold when the parison is located therein and to fasten thereto the components inside the tank without the edges of the parison being welded (since the core must be removed before the final molding of the tank, a step during which the welding of the parison sections is carried out). Such a part (core) is, for example, described in Patent GB 1 410 215, the content of which is for this purpose incorporated by reference into the present application.
However, during the implementation of these various improvements, the Applicant noticed that in certain cases the components were not in the molded and cooled tank, at the location at which the core had placed them on the parison. The Applicant has also observed in certain cases (for example, in the case of saddle tanks, in the restriction leading from one pocket to the other), a local degradation of the internal surface of the wall of the tank which, although not visible from the outside, may lead to a degradation of the FT performances as regards the impermeability.
After analyses of the various cases observed, the Applicant has finally found the source of the problem: in general, the lines (ventilation lines, fuel or electricity supply lines, etc.) are only fastened to the FT by their ends and/or by their active points (for example; by the ventilation valves in the case of ventilation lines) and they can therefore, when the mold is being closed for the definitive molding of the tank (after having removed therefrom the core which has fastened the components to the parison), come to press on the part of the parison opposite and/or close to them.
It should specifically be noted that in order to be able to compensate for the thermal expansions of the tank when in service, these lines are generally fastened loosely and may therefore make loops or have free lengths between their fastening points. In conventional FT manufacturing processes, where the lines are fastened to the molded and cooled tank, the presence of such loops is common and is not an obstruction. Conversely, in a process such as that described above where the lines are fastened when the parison is molten, these loops are in fact the cause of the aforementioned problem since they can rub against the parison (and weaken it) and/or against another accessory found therein (and move the latter relative to its ideal location).